Higher RPM with hotter sparkplug change?

4 posts / 744 viewsLast Reply July 7, 2008

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Guest Anonymous

Guest Anonymous

I have been running W7DC plugs gapped to .035 for ages. I was happy with them. I purchased W8DC plugs by mistake. Because they are also compatible with my stock 32/36 weber equipped vehicle, I decided to give them a try. Gapped at .040.

With just the change of spark plugs, idle speed increased by approximately 125 rpm at idle (according to my snapon digital tach.) Over the course of the weekend I swapped the new plugs for neatly filed and regapped older plugs and the idle dropped by the same amount. I repeated the experiment another 2 times with the same results. Needless to say I like having a higher idle apparently without additional fuel consumption. The only draw back with using these hotter plugs is that I notice pinging on hard acceleration. With the colder plugs the pinging is not there.

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Guest Anonymous

Guest Anonymous

Just curious - pinging a what rpm and load? Have you tried re-jetting to get rid of the pinging which might be a sign of slightly lean mixture that you could get away with using a colder plug?

Pinging occurs when throttle is mashed on incline at approximately 2500+RPM. It can be avoided by driving slower, using octane booster or retarding the timing. The colder plugs did not show any evidence of fouling and I had a preference for them simply because I tend to drive mostly on the interstate. It has been quite some time, but the carb was originally jetted with help of a dyno, so I am not terribly inclined to deviate much. I am now curious about trying other plugs I have lying around including NGK, Champion and Autolite.